1. Field of the Invention
The present invention relates to devices for the cleaning of screens located in a water conduit such as a sewer.
2. Description of the Prior Art
Devices for the cleaning of screens which are located in a water conduit are known which include a screen rake capable of being moved from an intermediate or rest position above the water surface into a meshing position with the screen, and then into a substantially horizontal position above a collecting bin for emptying, wherein the screen rake comprises a screen comb connected to a rake arm. The screen comb can be tilted about a horizontal axis and the rake arm can be pivoted about a horizontal pivot axis, the rake being pivoted and moved in a vertical plane by a drive device. The rake arm and drive device are located on the downstream side of the screen.
As shown in U.S. Pat. No. 3,909,411 the screen rake, including the rake arm, is arranged such that during all movement thereof the rake arm projects beyond the highest vertical positioning of the screen comb when in its emptying position, such that the overall height of the screen assembly is much less than in screen assemblies, for example as shown in German Pat. No. 709,881, wherein the rake arm projects far beyond the highest positioning of the screen comb when the screen comb is at its highest (emptying) position. According to the U.S. Patent noted, sufficient room is made available for the positioning of a large enough collecting bin to receive all of the screenings dumped by the screen comb.
The drive device in the aforementioned U.S. Patent, however, consists of a cylinder-piston units which engage in an articulated manner with the rake arm and with a crank arm hinged thereto, and these units are provided with control and pressure-limiting valves. Such a drive device is relatively costly and subject to operational difficulties, especially when operated by inexperienced personnel. This tends to be the case because the cylinder-piston units have to be operated alternatively in opposite directions during a single cleansing process.
The present invention has as an object the development of an improved cleaning device as disclosed in U.S. Pat. No. 3,909,411 wherein as low a structural height of the device as possible is maintained, and wherein the rake arm is operated by a simple, trouble-free mechanical control arrangement.